Measurement of semiconductor structures with capillary condensation

ABSTRACT

Methods and systems for performing optical measurements of geometric structures filled by a capillary condensation process are presented herein. Measurements are performed while the structures under measurement are treated with a flow of purge gas that includes a controlled amount of fill material. A portion of the fill material condenses onto the structures under measurement and fills openings in the structural features, spaces between structural features, small volumes such as notches, trenches, slits, contact holes, etc. The degree of saturation of vaporized material in the gaseous flow is adjusted based on the maximum feature size to be filled. In some examples, measurement data, such as spectroscopic data or image data, are collected when a structure is unfilled and when the structure is filled by capillary condensation. The collected data are combined to improve measurement performance.

CROSS REFERENCE TO RELATED APPLICATION

The present application for patent claims priority under 35 U.S.C. § 119from U.S. provisional patent application Ser. No. 62/330,751, entitled“Porosity and Critical Dimension Measurements Using Capillarycondensation,” filed May 2, 2016, and from U.S. provisional patentapplication Ser. No. 62/441,887, entitled “Critical DimensionMeasurements Using Liquid Filling,” filed Jan. 3, 2017, and from U.S.patent application Ser. No. 15/204,938, entitled “Critical DimensionMeasurements With Capillary Condensation,” filed Jul. 7, 2016, thesubject matter of each is incorporated herein by reference in itsentirety.

TECHNICAL FIELD

The described embodiments relate to metrology systems and methods, andmore particularly to methods and systems for improved measurement ofstructures fabricated in the semiconductor industry.

BACKGROUND INFORMATION

Semiconductor devices such as logic and memory devices are typicallyfabricated by a sequence of processing steps applied to a specimen. Thevarious features and multiple structural levels of the semiconductordevices are formed by these processing steps. For example, lithographyamong others is one semiconductor fabrication process that involvesgenerating a pattern on a semiconductor wafer. Additional examples ofsemiconductor fabrication processes include, but are not limited to,chemical-mechanical polishing, etch, deposition, and ion implantation.Multiple semiconductor devices may be fabricated on a singlesemiconductor wafer and then separated into individual semiconductordevices.

Metrology processes are used at various steps during a semiconductormanufacturing process to detect defects on wafers to promote higheryield. Model-based metrology techniques offer the potential for highthroughput without the risk of sample destruction. A number ofmodel-based metrology based techniques including scatterometry,ellipsometry, and reflectometry implementations and associated analysisalgorithms are commonly used to characterize critical dimensions, filmthicknesses, composition, overlay and other parameters of nanoscalestructures.

Modern semiconductor processes are employed to produce complexstructures. A complex measurement model with multiple parameters isrequired to represent these structures and account for process anddimensional variations. Complex, multiple parameter models includemodeling errors induced by parameter correlations and low measurementsensitivity to some parameters. In addition, regression of complex,multiple parameter models having a relatively large number of floatingparameter values may not be computationally tractable.

To reduce the impact of these error sources and reduce computationaleffort, a number of parameters are typically fixed in a model-basedmeasurement. Although fixing the values of a number of parameters mayimprove calculation speed and reduce the impact of parametercorrelations, it also leads to errors in the estimates of parametervalues.

Currently, the solution of complex, multiple parameter measurementmodels often requires an unsatisfactory compromise. Current modelreduction techniques are sometimes unable to arrive at a measurementmodel that is both computationally tractable and sufficiently accurate.Moreover, complex, multiple parameter models make it difficult, orimpossible, to optimize system parameter selections (e.g., wavelengths,angles of incidence, etc.) for each parameter of interest.

Future metrology applications present challenges due to increasinglysmall resolution requirements, multi-parameter correlation, increasinglycomplex geometric structures, and increasing use of opaque materials.Thus, methods and systems for improved measurements are desired.

SUMMARY

Methods and systems for performing optical measurements of geometricstructures filled by a capillary condensation process are presentedherein. Measurements are performed while the local environment aroundthe structures under measurement is treated with a flow of purge gasthat includes a controlled amount of fill material. A portion of thefill material (i.e., the condensate) condenses onto the structures undermeasurement and fills openings in the structural features, spacingbetween structural features, small volumes such as notches, trenches,slits, contact holes, etc.

In one aspect, the degree of saturation of vaporized material in thegaseous flow provided to the structures under measurement is adjustedbased on the maximum feature size to be filled by capillarycondensation.

In another aspect, measurements are performed with a data set includingmeasurement signals collected from structures having geometric featuresfilled with a condensate. The presence of the condensate changes theoptical properties of the structure under measurement compared to ameasurement scenario where the purge gas is devoid of any fill material.

In some examples, multiple measurements of a structure are performed fordifferent condensation states. Each measurement corresponds to adifferent amount of condensate condensed onto the structures undermeasurement. By collecting measurement signal information associatedwith a structure having geometric features filled with different amountsof condensate, parameter correlation among floating measurementparameters is reduced and measurement accuracy is improved.

In some examples, measurement data is collected when a structure isfilled from capillary condensation and measurement data is collectedfrom the same structure when the structure is not filled (i.e., notsubject to capillary condensation).

In some embodiments, the amount of fill material vaporized in a gaseousflow provided to the structures under measurement is regulated bycontrolling the partial pressure of the fill material in the gaseousflow. In some embodiments, a flow of unsaturated purge gas is mixed witha flow of saturated purge gas. The ratio of these flows is regulated toadjust the partial pressure of the fill material in the combined flow.

In some embodiments, a purge gas is bubbled through a liquid bath offill material to generate a flow of purge gas that is fully saturatedwith fill material. The partial pressure of the fill material vaporizedin the purge gas flow is equal to the equilibrium pressure of the fillmaterial over the liquid bath of the fill material.

In some embodiments, the liquid bath of fill material is maintained atthe same temperature as the specimen under measurement. In some otherembodiments, the liquid bath of fill material is maintained at a lowertemperature than the specimen under measurement.

In some embodiments, the degree of saturation of the vaporized fillmaterial at the wafer is controlled by adding an involatile solute in aliquid bath of fill material that suppresses the equilibrium vaporpressure of the fill material. In these embodiments, the degree ofsaturation of the vaporized fill material is regulated by controllingthe concentration of solute in solution.

In some embodiments, the fill material exhibits fluorescence in responseto the illumination light provided to the structures under measurementto enhance measurement contrast, particularly in image based measurementapplications.

The foregoing is a summary and thus contains, by necessity,simplifications, generalizations and omissions of detail; consequently,those skilled in the art will appreciate that the summary isillustrative only and is not limiting in any way. Other aspects,inventive features, and advantages of the devices and/or processesdescribed herein will become apparent in the non-limiting detaileddescription set forth herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrative of a system 100 for measuringstructures of a semiconductor wafer subject to capillary condensation.

FIG. 2 is a diagram illustrative of a vapor injection system 120 ofsystem 100 in one embodiment.

FIG. 3 is a diagram illustrative of a vapor injection system 120 ofsystem 100 in another embodiment.

FIG. 4 depicts a table 127 including the enthalpy of vaporization, ΔH,of water, toluene, and ethanol. In addition, table 127 illustrates thedifference between a wafer temperature and a temperature of a bath ofliquid fill material to achieve a relative saturation of the fillmaterial of 0.9 at the wafer.

FIG. 5 depicts a plot 128 of the partial pressure of water as a functionof concentration of hydrochloric acid in the bath of water.

FIG. 6 depicts a plot 135 of dispersion characteristics of de-ionizedwater as a function of wavelength.

FIG. 7 depicts a table 129 illustrating the molar volume and surfacetension associated with water, toluene, and ethanol.

FIG. 8 depicts a plot 172 illustrating the maximum diameter of acylindrical hole that can be filled by capillary condensation atdifferent partial pressures in accordance with Kelvin's equation forwater, ethanol, and toluene as fill materials.

FIG. 9 depicts a plot 160 illustrating the maximum diameter of a long,trench-like feature that can be filled by capillary condensation atdifferent partial pressures in accordance with Kelvin's equation forwater, ethanol, and toluene as fill materials.

FIG. 10 illustrates an unfilled line-space metrology target having aperiodic, two dimensional, resist grating structure fabricated on asubstrate.

FIG. 11 illustrates the line-space metrology target illustrated in FIG.10 filled with a fill material.

FIG. 12A illustrates an unfilled, metrology target having multiplelayers, including a top layer having a cylindrical contact hole.

FIG. 12B illustrates the metrology target illustrated in FIG. 10A withthe cylindrical contact hole filled with a fill material.

FIG. 13 depicts a comparison of measurement results obtained withoutshape filling and measurement results obtained with a multi-target modelusing data collected with and without shape filling for a number ofparameters of the metrology target depicted in FIG. 10A.

FIG. 14 illustrates a method 200 for performing measurements ofstructures subject to capillary condensation in one example.

FIG. 15 depicts a chart 210 of the relative humidity, RH, for differentcombinations of flows F₁ and F₂ as defined with respect to equation (1).

FIG. 16 depicts a plot 220 of the spectroscopic ellipsometry parameter,α, for measurements of the same structure in both unfilled and filledstates.

FIG. 17 depicts a plot 230 of the spectral difference between thespectroscopic ellipsometry measurements depicted in FIG. 16.

FIG. 18 depicts a plot 240 of the spectroscopic ellipsometry parameter,β, for measurements of the same structure in both unfilled and filledstates.

FIG. 19 depicts a plot 250 of the spectral difference between thespectroscopic ellipsometry measurements depicted in FIG. 18.

DETAILED DESCRIPTION

Reference will now be made in detail to background examples and someembodiments of the invention, examples of which are illustrated in theaccompanying drawings.

Methods and systems for performing optical measurements of geometricstructures filled with a condensate by a capillary condensation processare presented herein. Model based measurements are performed with anenriched data set including measurement signals collected from ametrology target having geometric features filled with a condensate.This reduces parameter correlation among floating measurement parametersand improves measurement accuracy. Thus, sufficiently accuratemodel-based measurement results can be obtained, and often with reducedcomputational effort.

Measurements are performed while the local environment around themetrology target under measurement is treated with a flow of purge gasthat includes a controlled amount of fill material. A portion of thefill material (i.e., the condensate) condenses onto the structures undermeasurement and fills openings in the structural features, openingsbetween structural features, etc. The presence of the condensate changesthe optical properties of the structure under measurement compared to ameasurement scenario where the purge gas is devoid of any fill material.

In some examples, multiple measurements of the metrology target areperformed for different condensation states. In other words, eachmeasurement corresponds to a different amount of condensate condensedonto the structures under measurement. By collecting measurement signalinformation associated with a metrology target having geometric featuresfilled with different amounts of condensate, model based measurementsare performed with an enriched set of measurement data.

In one example, measurement data is collected when a structure isunfilled and additional measurement data is collected when the samestructure is filled by capillary condensation. The collected data iscombined in a multi-target model based measurement to estimate the valueof one or more parameters of interest with reduced parameter correlationand improved measurement performance.

FIG. 1 illustrates a system 100 for measuring characteristics of asemiconductor wafer. As shown in FIG. 1, the system 100 may be used toperform spectroscopic ellipsometry measurements of one or morestructures 114 of a semiconductor wafer 112 disposed on a waferpositioning system 110. In this aspect, the system 100 may include aspectroscopic ellipsometer 101 equipped with an illuminator 102 and aspectrometer 104. The illuminator 102 of the system 100 is configured togenerate and direct illumination of a selected wavelength range (e.g.,100-2500 nm) to the structure 114 disposed on the surface of thesemiconductor wafer 112. In turn, the spectrometer 104 is configured toreceive light from the surface of the semiconductor wafer 112. It isfurther noted that the light emerging from the illuminator 102 ispolarized using a polarization state generator 107 to produce apolarized illumination beam 106. The radiation reflected by thestructure 114 disposed on the wafer 112 is passed through a polarizationstate analyzer 109 and to the spectrometer 104. The radiation receivedby the spectrometer 104 in the collection beam 108 is analyzed withregard to polarization state, allowing for spectral analysis ofradiation passed by the analyzer. The detected spectra 111 are passed tothe computing system 130 for analysis of the structure 114.

Computing system 130 is configured to receive measurement data 111associated with a measurement (e.g., critical dimension, film thickness,composition, process, etc.) of the structure 114 of specimen 112 that isfilled due to capillary condensation. In one example, the measurementdata 111 includes an indication of the measured spectral response of thespecimen by measurement system 100 based on the one or more samplingprocesses from the spectrometer 104. In some embodiments, computingsystem 130 is further configured to determine specimen parameter valuesof structure 114 from measurement data 111. In one example, thecomputing system 130 is configured to access model parameters inreal-time, employing Real Time Critical Dimensioning (RTCD), or it mayaccess libraries of pre-computed models for determining a value of atleast one parameter of interest associated with the target structure114. In some embodiments, the estimated values of the one or moreparameters of interest are stored in a memory (e.g., memory 132). In theembodiment depicted in FIG. 1, the estimated values 115 of the one ormore parameters of interest are communicated to an external system (notshown).

In general, ellipsometry is an indirect method of measuring physicalproperties of the specimen under inspection. In most cases, the rawmeasurement signals (e.g., α_(meas) and β_(meas)) cannot be used todirectly determine the physical properties of the specimen. The nominalmeasurement process consists of parameterization of the structure (e.g.,film thicknesses, critical dimensions, material properties, etc.) andthe machine (e.g., wavelengths, angles of incidence, polarizationangles, etc.). A measurement model is created that attempts to predictthe measured values (e.g., α_(meas) and β_(meas)). As illustrated inequations (1) and (2), the model includes parameters associated with themachine (P_(machine)) and the specimen (P_(specimen)).α_(model) =f(P _(machine) ,P _(specimen))  (1)β_(model) =g(P _(machine) ,P _(specimen))  (2)

Machine parameters are parameters used to characterize the metrologytool (e.g., ellipsometer 101). Exemplary machine parameters includeangle of incidence (AOI), analyzer angle (A₀), polarizer angle (P₀),illumination wavelength, numerical aperture (NA), compensator orwaveplate (if present), etc. Specimen parameters are parameters used tocharacterize the specimen (e.g., specimen 112 including structures 114).For a thin film specimen, exemplary specimen parameters includerefractive index, dielectric function tensor, nominal layer thickness ofall layers, layer sequence, etc. For a CD specimen, exemplary specimenparameters include geometric parameter values associated with differentlayers, refractive indices associated with different layers, etc. Formeasurement purposes, the machine parameters are treated as known, fixedparameters and one or more of the specimen parameters are treated asunknown, floating parameters.

In some examples, the floating parameters are resolved by an iterativeprocess (e.g., regression) that produces the best fit betweentheoretical predictions and experimental data. The unknown specimenparameters, P_(specimen), are varied and the model output values (e.g.,α_(model) and β_(model)) are calculated until a set of specimenparameter values are determined that results in a close match betweenthe model output values and the experimentally measured values (e.g.,α_(meas) and β_(meas)). In a model based measurement application such asspectroscopic ellipsometry on a CD specimen, a regression process (e.g.,ordinary least squares regression) is employed to identify specimenparameter values that minimize the differences between the model outputvalues and the experimentally measured values for a fixed set of machineparameter values.

In some examples, the floating parameters are resolved by a searchthrough a library of pre-computed solutions to find the closest match.In a model based measurement application such as spectroscopicellipsometry on a CD specimen, a library search process is employed toidentify specimen parameter values that minimize the differences betweenpre-computed output values and the experimentally measured values for afixed set of machine parameter values.

In some other examples, model-based library regression or a signalresponse metrology model are employed to estimate values of parametersof interest.

In a model-based measurement application, simplifying assumptions oftenare required to maintain sufficient throughput. In some examples, thetruncation order of a Rigorous Coupled Wave Analysis (RCWA) must bereduced to minimize compute time. In another example, the number orcomplexity of library functions is reduced to minimize search time. Inanother example, the number of floating parameters is reduced by fixingcertain parameter values. In some examples, these simplifyingassumptions lead to unacceptable errors in the estimation of values ofone or more parameters of interest (e.g., critical dimension parameters,overlay parameters, etc.). By performing measurements of structuressubject to capillary condensation as described herein, the model-basedmeasurement model can be solved with reduced parameter correlations andincreased measurement accuracy.

As depicted in FIG. 1, metrology system 100 includes a vapor injectionsystem 120 configured to provide a gaseous flow 126 to structure 114during measurement. In one aspect, gaseous flow 126 includes a purge gasand a fill material vaporized in the purge gas. When the gaseous flowcomes into contact with the structure 114, condensation takes place anda portion of the fill material (i.e., the condensate) condenses ontostructure 114 under measurement. The condensate fills at least a portionof one or more structural features of the structure 114. The presence ofthe condensate changes the optical properties of the measured structure.

In some embodiments, a measurement is performed when the purge gas flowdoes not include fill material (e.g., pure nitrogen gas or clean dryair), and another measurement is performed when the purge gas flowincludes fill material such that the condensate completely fills theopenings between the structural features under measurement. Themeasurement data collected from these two measurements is communicatedto computing system 130 and an estimate of one or more structuralparameters of interest is made based on both sets of measurement data.

In some embodiments, a series of measurements are performed underdifferent condensation conditions such that the amount of condensationonto the structural features under measurement is different for eachmeasurement. The measurement data collected from the series ofmeasurements is communicated to computing system 130 and an estimate ofone or more structural parameters of interest is made based on thecollected measurement data.

As depicted in FIG. 1, an amount of fill material 123 is transportedfrom a fill material source 121 to the vapor injection system 120. Inaddition, a flow of purge gas 124 is transported from a purge gas source122 to the vapor injection system. Vapor injection system 120 causesfill material to vaporize into the flow of purge gas to generate thegaseous flow 126 provided to structure 114 under measurement. In theembodiment depicted in FIG. 1, the flow of purge gas and the amount offill material vaporized into the flow of purge gas is controlled bycommand signals 125 communicated from computing system 130 to vaporinjection system 120. Thus, command signals 125 control the desiredcomposition of gaseous flow 126. As depicted in FIG. 1, gaseous flow 126passes through nozzle 105 that directs gaseous flow 126 to the desiredlocation on wafer 110 with the appropriate flow characteristics. In someembodiments, nozzle 105 is located in close proximity to the measurementarea to transfer fill material to an area encompassing the structuresunder measurement. After measurement, the condensed fill materialevaporates into a general, wafer-level purge gas flow and is transportedaway from the wafer. In some examples, gaseous flow 126 is provided towafer 112 at a flow rate between one and two thousand standard cubiccentimeters per minute (SCCM). However, in general, any suitable flowrate may be contemplated within the scope of this patent document.

FIG. 1 depicts gaseous flow 126 provided locally to the metrology targetunder measurement. However, in general, gaseous flow 126 may be providedover the entire wafer, through any portion of the beam path from theillumination source to the detector, or any combination thereof. Variousexamples of providing purge gas flow over the wafer and through the beampath between the illumination source and the detector are described inU.S. Pat. No. 7,755,764, by Hidong Kwak, et al., and issued on Jul. 13,2010, the subject matter of which is incorporated herein by reference inits entirety.

As depicted in FIG. 1, vapor injection system 120 causes fill material123 to vaporize into a flow of purge gas 124 to generate gaseous flow126 provided to structure 114 under measurement. However, in general,vapor injection system 120 may control the vaporization of two or moredifferent fill materials into a flow of purge gas to generate a gaseousflow provided to structure 114 under measurement. In this manner, vaporinjection system 120 provides a gaseous flow 126 to wafer 112 thatincludes controlled amounts of different fill materials.

The embodiments of the system 100 illustrated in FIG. 1 may be furtherconfigured as described herein. In addition, the system 100 may beconfigured to perform any other block(s) of any of the methodembodiment(s) described herein.

FIG. 2 is a diagram illustrative of vapor injection system 120 in oneembodiment. In this embodiment, the amount of fill material vaporized ingaseous flow 126 provided to wafer 112 under measurement (i.e., thepartial pressure of the condensate) is regulated. By regulating thepartial pressure of the fill material, the structural dimensions filledby capillary condensation are controlled.

In the embodiment depicted in FIG. 2, the partial pressure of the fillmaterial vaporized in the purge gas flow (e.g., nitrogen gas, clean, dryair, etc.) is equal to the equilibrium pressure of the fill materialover a liquid bath of the fill material through which the purge gas isbubbled. In one example, a bubbler-type vapor injection system is a 1.2liter capacity stainless steel bubbler, model Z553360, commerciallyavailable from Sigma-Aldrich, St. Louis, Mo. (USA).

As depicted in FIG. 2, a portion 146 of purge gas flow 124 passesthrough mass flow controller 148A and another portion 145 of purge gasflow 124 passes through mass flow controller 148B. The flow rates ofgaseous flows 146 and 145 are controlled by the state of mass flowcontrollers 148A and 148B, respectively. In this manner, the amount ofpurge gas flow 124 into which fill material is vaporized is controlledby mass flow controller 148B and the amount of purge gas flow 124 thatis not subject to vaporization is controlled by mass flow controller148B. In the embodiment depicted in FIG. 2, command signal 125communicated from computing system 130 to vapor injection system 120includes multiple signals 149A-C. Signal 149A includes an indication ofthe desired state of mass flow controller 148A. In response, mass flowcontroller 148A adjusts to the desired position, and thus, the desiredproportion of purge gas flow into which no fill material is vaporized.Signal 149B includes an indication of the desired state of mass flowcontroller 148B. In response, mass flow controller 148B adjusts to thedesired state, and thus, the desired proportion of purge gas flow intowhich fill material is vaporized. Portion 145 of purge gas flow 124passes through a check valve 142, a mass flow controller 143, and intobubbler 140. In bubbler 140, an amount of fill material is vaporizedinto portion 145 of purge gas flow 124 to generate a gaseous flow 147 ofpurge gas and fill material. Gaseous flow 147 is combined with theportion 146 of purge gas that did not flow through bubbler 140 togenerate gaseous flow 126.

In some embodiments, mass flow controllers 148A and 148B are controlledsuch that the entirety of purge gas flow 124 either flows throughbubbler 140 or by-passes bubbler 140 completely. In this manner, gaseousflow 126 is either a dry purge gas flow 124 having zero partial pressureof fill material or the entire purge gas flow 124 is subject tovaporization of fill material.

As fill material is vaporized in bubbler 140 and carried away as gaseousflow 147, additional fill material 123 flows from fill material source121 to maintain a constant fill level in bubbler 140. In someembodiments, the fill level is automatically controlled based on a levelsensor and flow control scheme. In some other embodiments, the filllevel is periodically maintained by a manual filling operation.

In one embodiment, the degree of saturation of the vaporized fillmaterial in gaseous flow 126 at an ambient temperature, T_(a), iscontrolled by adjusting the proportion of purge gas flow 145 into whichfill material is vaporized relative to the portion of purge gas flow 146that is not subject to vaporization. In a preferred embodiment, thetemperature of the fill material in bubbler 140 is maintained at thesame temperature as the wafer under measurement (e.g., ambienttemperature, T_(a)). Under these conditions, the relative saturation ofthe fill material in gaseous flow 126, p₀/p, is described in equation(1), where F₁ is the flow rate of fully saturated gaseous flow 147 andF₂ is the flow rate of unsaturated gaseous flow 146.

$\begin{matrix}{\frac{p}{p_{0}} = \frac{F_{1}}{\left( {F_{1} + F_{2}} \right)}} & (1)\end{matrix}$

As illustrated in FIG. 2, gaseous flows 146 and 147 are combined to formgaseous flow 126 provided to the wafer under measurement. Thus, thetotal flow provided to the wafer under measurement is controlled bycommunicating command signals 149A and 149B to regulate the sum of F₁and F₂. The relative saturation of the flow provided to the wafer undermeasurement is controlled by communicating command signals 149A and 149Bto regulate the ratio of F₁ and F_(2.)

FIG. 15 depicts a chart 210 of the relative humidity, RH, for differentcombinations of flows F₁ and F₂ as defined with respect to equation (1).

In another embodiment, the degree of saturation of the vaporized fillmaterial at an ambient temperature, T_(a), is controlled by maintainingthe liquid bath at a temperature, T, below the ambient temperature. Therelationship between equilibrium vapor pressure, p₀, of a pure substanceand temperature, T, is given by the Clausius-Clapyron equationillustrated by equation (2), where ΔH is the enthalpy of vaporization ofthe pure substance and R is the ideal gas constant, which is8.31J/mole·° K.

$\begin{matrix}{\frac{d\mspace{11mu}\ln\mspace{11mu}\left( p_{0} \right)}{d\left( \frac{1}{T} \right)} = {- \frac{\Delta\; H}{R}}} & (2)\end{matrix}$

Based on equation (2), the relative saturation, p/p₀, for a fillmaterial saturated at a temperature, T, which is less than the ambienttemperature, Ta, is illustrated by equation (3).

$\begin{matrix}{{\ln\left( \frac{p}{p_{0}} \right)} = {\frac{\Delta\; H}{R}\left( {\frac{1}{T_{a}} - \frac{1}{T}} \right)}} & (3)\end{matrix}$

FIG. 4 depicts a table 127 including the enthalpy of vaporization, ΔH,of water, toluene, and ethanol. Each of these substances may be suitableas fill materials as described herein. In addition, table 127illustrates the difference between the ambient temperature (i.e., wafertemperature) and the bath temperature when the ambient temperature is 25degrees Centigrade and the desired relative saturation of the fillmaterial, p/p₀, is 0.9. As illustrated in table 127, by maintaining thebath temperature below the ambient temperature by the illustratedamounts, a partial pressure at 0.9 is maintained for each listed fillmaterial. It may be advantageous to utilize any of these substances asfill materials because it is a relatively simple matter to maintain atemperature differential of approximately two degrees Centigrade betweenthe wafer and the liquid bath of bubbler 140. In this embodiment, it ispossible to control the degree of saturation of the vaporized fillmaterial in gaseous flow 126 at an ambient temperature, T_(a), withoutcombining a flow of dry purge gas 146 with the flow of saturated purgegas 147. In other words, flow 146 can be set to zero, and the degree ofsaturation of the vaporized fill material in gaseous flow 126 at anambient temperature, T_(a), is controlled by the temperature differencebetween the bubbler temperature and the wafer temperature. In some otherexamples, a flow of dry purge gas 146 is combined with the flow ofsaturated purge gas 147, and the degree of saturation of the vaporizedfill material in gaseous flow 126 at an ambient temperature, T_(a), iscontrolled by a combination of a temperature difference between thebubbler temperature and the wafer temperature and the ratio of theflowrates of gaseous flow 146 and gaseous flow 147.

In some embodiments, the bath temperature and wafer temperature aremeasured and communicated to computing system 130. Computing systemdetermines a difference between the wafer temperature and the bathtemperature and calculates a desired wafer temperature, bathtemperature, or both. In some embodiments, computing system 130generates a command signal 149C indicative of a desired bath temperatureto vapor injection system 120. In response, vapor injection system 120adjusts the bath temperature to the desired value using a local heatingor cooling unit (not shown). In some embodiments, computing system 130generates a command signal (not shown) indicative of a desired wafertemperature to a wafer conditioning subsystem (not shown). In response,the wafer conditioning subsystem adjusts the wafer temperature to thedesired value using a wafer heating or cooling unit (not shown). In someembodiments, computing system 130 generates a command signal 113(depicted in FIG. 1) indicative of a desired wafer temperature to alocal wafer heating element 103. In response, the heating unit 103adjusts the wafer temperature locally (i.e., in the immediate vicinityof the measurement location) to the desired value using a radiativeheating element.

In some embodiments, control of the temperature difference between thewafer and the bath is controlled by a computing system associated withvapor injection system 120. In this sense, control of the temperaturedifference between the wafer and the bath by computing system 130 isprovided by way of non-limiting example. Any suitable controlarchitecture and temperature regulation scheme may be contemplatedwithin the scope of this patent document.

FIG. 3 is a diagram illustrative of vapor injection system 120 inanother embodiment. Like numbered elements are analogous to thosedescribed with reference to FIG. 2.

As depicted in FIG. 3, the flow of purge gas 124 passes through athree-way valve 141. In some embodiments, three-way valve 141proportions a portion 145 of purge gas flow 124 that flows throughbubbler 140 with a portion 146 that does not flow through bubbler 140based on a position of the three-way valve. In this manner, the amountof purge gas flow 124 into which fill material is vaporized iscontrolled by three-way valve 141. In the embodiment depicted in FIG. 3,command signal 125 communicated from computing system 130 to vaporinjection system 120 includes multiple signals 149C-D. In the embodimentdepicted in FIG. 3, signal 149D includes an indication of the desiredposition of three-way valve 141. In response, three-way valve 141adjusts to the desired position, and thus, the desired proportion ofpurge gas flow into which fill material is vaporized. Portion 145 ofpurge gas flow 124 passes through a check valve 142, a mass flowcontroller 143, and into bubbler 140. In bubbler 140, an amount of fillmaterial is vaporized into portion 145 of purge gas flow 124 to generatea gaseous flow 147 of purge gas and fill material. Gaseous flow 147 iscombined with the portion 146 of purge gas that did not flow throughbubbler 140 to generate gaseous flow 126.

In some embodiments, three-way valve 141 is controlled such that theentirety of purge gas flow 124 either flows through bubbler 140 orby-passes bubbler 140 completely based on a position of the three-wayvalve. In this manner, gaseous flow 126 is either a dry purge gas flow124 having zero partial pressure of fill material or the entire purgegas flow 124 is subject to vaporization of fill material depending onthe state of three-way valve 141.

As described with reference to FIG. 3, the amount of fill materialprovided to the wafer under measurement is controlled by regulating theportion 145 of purge gas flow 124 that is subject to vaporization offill material relative to the portion 146 of purge gas flow 124 that isnot. In addition, the degree of saturation of the vaporized fillmaterial at wafer temperature is controlled by regulating the differencebetween the wafer temperature and the bath temperature.

In another embodiment, the degree of saturation of the vaporized fillmaterial at ambient temperature is controlled by adding an involatilesolute in a liquid bath of solvent (i.e., fill material) that suppressesthe equilibrium vapor pressure of the solvent compared to theequilibrium vapor pressure of the solvent alone. In one example, asolution formed from water as the solvent and an involatile solute(e.g., sodium chloride, hydrochloric acid, etc.) exhibits a vaporpressure of water that is less than the equilibrium vapor pressure ofpure water. FIG. 5 depicts a plot 128 of the partial pressure of wateras a function of concentration of hydrochloric acid in the bath ofwater. A similar result exists for a solution of sodium chloridedissolved in water. For example, a solution of six percent sodiumchloride dissolved in water yields a relative humidity, p/p₀, of 90%.

In these embodiments, the degree of saturation of the vaporized fillmaterial (i.e., the solvent) is regulated by controlling theconcentration of solute in solution. In some embodiments, the amount ofsolvent in the bath is controlled to maintain the desired concentration,and thus the desired partial pressure of the vaporized solvent. In theseembodiments, precise temperature control is not necessary as long as thebath temperature is maintained nominally at the ambient temperature(i.e., wafer temperature).

In general, any suitable purge gas and fill material may be selected foruse in performing measurements as described herein. Exemplary purgegases include inert gases, nitrogen, and clean dry air. The selection ofsuitable purge gas is driven primarily by availability in asemiconductor fabrication facility. Exemplary fill materials includewater, ethanol, isopropyl alcohol, methanol, benzene, toluene, etc. Theselection of suitable fill materials is driven by the ability to controlvapor pressure, void filling characteristics, optical characteristics,and any chemical interactions between the fill material and the specimenunder measurement.

For example, both the index of refraction of the fill material and theabsorption coefficient of the fill material are considered in theunderlying measurement model as the liquid fill material not onlyrefracts incident light, but also absorbs incident light. Both of thesecharacteristics create differences between measurements performed withfill and measurements performed without fill, particularly at relativelyshort illumination wavelengths (e.g., vacuum ultraviolet wavelengthsranging from 120 nanometers to 190 nanometers). Thus, a selection of aliquid fill material that differs substantially from air in both indexof refraction and absorption coefficient offers the opportunity forreduced parameter correlations in a multi-target measurement analysis.

In addition, a selection of a liquid fill material that varies in bothindex of refraction and absorption coefficient as a function ofillumination wavelength offers the opportunity for reduced parametercorrelations in a spectral measurement analysis. FIG. 6 depicts a plot135 of the dispersion of de-ionized water as a function of wavelength.Plotline 136 depicts the extinction coefficient and plotline 137 depictsthe index of refraction. As depicted in FIG. 6, de-ionized waterexhibits strong dispersion changes in the ultraviolet, vacuumultraviolet and deep ultraviolet regions as well as in the infraredregions. Spectroscopic instruments that operate in these wavelengthranges exploit the dispersion changes when water is used as a condensatein periodic structures.

In some embodiments, measurements are performed using de-ionized wateras the fill material with a number of different spectral metrologytechniques that capture a wide range of wavelengths between 100nanometers and 2,500 nanometers. Exemplary metrology techniques includespectroscopic ellipsometry, mueller-matrix ellipsometry, spectroscopicreflectometry, angle-resolved reflectometry, etc.

In a further aspect, a selection of a liquid fill material that exhibitsfluorescence at illumination wavelengths offers the opportunity forreduced parameter correlations in image based measurement analyses. Insome embodiments, fluorescence of the fill material enhances imagecontrast and improves measurement performance of image based measurementtechniques such as image based overlay, image based inspection (e.g.,dark field and bright field inspection), etc.

In a further aspect, capillary condensation is employed to fill spacesbetween geometric, structural features of a metrology target itself(e.g., a critical dimension (CD) structures, grating structures, overlaystructures, etc.) during measurement of the metrology target bycapillary condensation. In general, the desired degree of saturation ofvaporized material in gaseous flow 126 is determined based on themaximum feature size to be filled by capillary condensation. Capillarycondensation is employed to fill small features (e.g., small volumessuch as notches, trenches, slits, contact holes, etc.) with a fillmaterial. Kelvin's equation provides an approximation of the maximumfeature size that can be filled for a particular fill material, partialpressure of the fill material, and ambient temperature (e.g., wafertemperature). Equation (3) illustrates Kelvin's equation for a condensedmeniscus having two different radii, r₁ and r₂, where, R, is the idealgas constant, T_(a), is the ambient temperature, V, is the molar volumeof the fill material, γ, is the surface tension constant associated withthe fill material, and p/p₀, is the partial pressure of the fillmaterial.

$\begin{matrix}{{\frac{1}{r_{1}} + \frac{1}{r_{2}}} = {\frac{{RT}_{a}}{\gamma\; V}{\ln\left( \frac{p}{p_{0}} \right)}}} & (3)\end{matrix}$

FIG. 7 depicts a table 129 illustrating the molar volume and surfacetension associated with water, toluene, and ethanol.

For cylindrical hole features, r₁ equals r₂. FIG. 8 depicts a plot 172illustrating the maximum diameter of a cylindrical hole that can befilled by capillary condensation in accordance with equation (3). Plot172 depicts the maximum diameter of a cylindrical hole that can befilled by water (plotline 175), ethanol (plotline 174), and toluene(plotline 173) for various partial pressures of each fill material at anambient temperature of 25 degrees Centigrade. As depicted in FIG. 8,cylindrical holes having diameters up to 40 nanometers may be filledwhen gaseous flow 126 is provided to the metrology target with a partialpressure of water or ethanol of 95% or higher. Also as depicted in FIG.8, cylindrical holes having diameters up to 90 nanometers may be filledwhen gaseous flow 126 is provided to the metrology target with a partialpressure of toluene of 95% or higher.

For lines and spaces, r₂, is zero. FIG. 9 depicts a plot 160illustrating the maximum diameter of a long, trench-like feature thatcan be filled by capillary condensation in accordance with equation (3).Plot 160 depicts the maximum diameter of a trench that can be filled bywater (plotline 164), ethanol (plotline 163), and toluene (plotline 162)for various partial pressures of each fill material at an ambienttemperature of 25 degrees Centigrade. As illustrated, the maximumdiameter across a long, trench-like feature is half the maximum diameterof a cylindrical hole feature. As depicted in FIGS. 8 and 9, theplotlines of water and ethanol appear to overlap because the performanceof ethanol as a fill material is very similar to water.

In one aspect, the degree of saturation of the vaporized fill materialat an ambient temperature, T_(a), is adjusted such that all featuresbelow a desired maximum feature size are filled. In some embodiments,this is achieved by controlling the ratio of a flow of purge gas subjectto vaporization and a flow of purge gas that is not subject tovaporization as described hereinbefore. In some embodiments, this isachieved by controlling the temperature difference between the wafer andthe liquid bath of fill material. In some other embodiments, this isachieved by controlling the concentration of involatile solute dissolvedin the liquid bath of fill material.

In a further aspect, measurements are performed at different degrees ofsaturation of the vaporized fill material at the ambient temperaturesuch that all features below a range of maximum feature sizes arefilled. The measurements are combined in a multi-target model basedmeasurement to estimate the value of one or more parameters of interestwith reduced parameter correlation and improved measurement performance.

FIG. 10 illustrates an unfilled line-space metrology target 150 having aperiodic, two dimensional, resist grating structure 152 fabricated on asubstrate 151. Grating structure 152 has a nominal top criticaldimension (TCD) of 7 nanometers and a height, H, of 50 nanometers.

FIG. 11 illustrates a filled line-space metrology target 155. Line-spacemetrology target 155 includes the same periodic, two dimensional, resistgrating structure 152 fabricated on a substrate 151, however, the spacesbetween the resist grating structure 152 are filled with a fill material153. This may be achieved, in one example, by providing gaseous flow 126to metrology target 155 including toluene at a partial pressure ofapproximately 70% or higher. In another example, filling of gratingstructure 152 may be achieved by providing gaseous flow 126 to metrologytarget 155 including water or ethanol at a partial pressure ofapproximately 85% or higher.

FIG. 12A depicts an unfilled, metrology target 156 having multiplelayers, including a top layer having a cylindrical contact hole. Asillustrated in FIG. 12A, metrology target 156 includes a first layer,166, a second layer, 167, a third layer, 168, and a fourth layer, 169,having a nominal height of 135 nanometers. The fourth layer includes acylindrical hole feature 170 through the fourth layer having a nominaldiameter of 10 nanometers. The structure of metrology target 165 has anominal width of 40 nanometers and a nominal length of 40 nanometers.

FIG. 12B depicts a filled metrology target 157 including the samemetrology target 156, except that the cylindrical hole 170 is filledwith an amount of fill material 171. This may be achieved, in oneexample, by providing gaseous flow 126 to metrology target 156 includingtoluene at a partial pressure of approximately 85% or higher. In anotherexample, filling of cylindrical hole 170 may be achieved by providinggaseous flow 126 to metrology target 155 including water or ethanol at apartial pressure of approximately 95% or higher.

The metrology targets depicted in FIGS. 10-12B are provided by way ofnon-limiting example. In general, a measurement site includes one ormore metrology targets measured by a measurement system (e.g., metrologysystem 100 depicted in FIG. 1). In general, measurement data collectionmay be performed across the entire wafer or a subset of the wafer area.In addition, in some embodiments, the metrology targets are designed forprintability and sensitivity to changes in process parameters,structural parameters of interest, or both. In some examples, themetrology targets are specialized targets. In some embodiments, themetrology targets are based on conventional line/space targets. By wayof non-limiting example, CD targets, SCOL targets, or AiM™ targetsavailable from KLA-Tencor Corporation, Milpitas, Calif. (USA) may beemployed. In some other embodiments, the metrology targets aredevice-like structures. In some other examples, the metrology targetsare device structures, or portions of device structures. Regardless ofthe type of metrology target employed, a set of metrology targets thatexhibit sensitivity to the process variations, structural variations, orboth, being explored is measured using shape filling by capillarycondensation as described herein.

In another aspect, measurement data is collected from structures (e.g.,CD structures, overlay structures, etc.) when the structures are filled(i.e., subject to capillary condensation as described herein) and whenthey are not filled (i.e., not subject to capillary condensation). Thecollected data is combined in a multi-target model based measurement toimprove measurement performance. In one example, measurement data iscollected when metrology target 156 is unfilled as depicted in FIG. 12A.In this scenario, a gaseous flow 126 is provided to metrology target 156without fill material vaporized into the flow. In addition, measurementdata is collected when metrology target 156 is filled as depicted inFIG. 12B. In this scenario, a gaseous flow 126 is provided to metrologytarget 156 with sufficient saturation of fill material to fillcylindrical hole 170 as described with reference to FIG. 12B. Thecollected data is received by computing system 130. Computing system 130performs a model based measurement analysis utilizing both sets ofmeasurement data with a multi-target model to estimate the values ofparameters of interest. In some examples, the multi-target modeldescribed herein is implemented off-line, for example, by a computingsystem implementing AcuShape® software available from KLA-TencorCorporation, Milpitas, Calif., USA. The resulting, multi-target model isincorporated as an element of an AcuShape® library that is accessible bya metrology system performing measurements using the multi-target model.

FIG. 13 depicts a comparison of measurement results obtained withoutshape filling and measurement results obtained with a multi-target modelusing data collected with and without shape filling for a number ofparameters of metrology target 156 depicted in FIG. 12A. Parameter L1_HTrefers to the height of the first layer 166 of metrology target 156depicted in FIG. 12A. L2_HT refers to the height of the second layer167. L3_HT refers to the height of the third layer 168. G4_TCD refers tothe top critical dimension of cylindrical hole 170. G4_BCD refers to thebottom critical dimension of cylindrical hole 170. G4_EL refers to theellipticity of cylindrical hole 170. As depicted in FIG. 13, theimprovement in measurement precision of each of L1_HT, L2_HT, L3_HT,G4_TCD, G4_BCD, and G4_EL is improved by a significant percentage asillustrated by measurement bars 177A-F, respectively. Similarly,measurement correlation of each of L1_HT, L2_HT, L3_HT, G4_TCD, G4_BCD,and G4_EL is improved (i.e., reduced) by a significant percentage asillustrated by measurement bars 178A-F, respectively.

FIG. 16 depicts a plot 220 of the spectroscopic ellipsometry parameter,α, for measurements of the same structure in both unfilled and filledstates. Plotline 221 depicts the spectral results for the measurementscenario when the structures are unfilled. Plotline 222 depicts thespectral results for the measurement scenario when the structures arefilled.

FIG. 17 depicts a plot 230 of the spectral difference between thespectroscopic ellipsometry measurements depicted in FIG. 16. Plotline231 depicts the difference between measurement results for theparameter, α. As depicted in FIG. 17, the spectral differences are quitedramatic. These data sets are effectively employed in a multi-targetanalysis to break correlations and improve measurement performance.

FIG. 18 depicts a plot 240 of the spectroscopic ellipsometry parameter,β, for measurements of the same structure in both unfilled and filledstates. Plotline 241 depicts the spectral results for the measurementscenario when the structures are unfilled. Plotline 242 depicts thespectral results for the measurement scenario when the structures arefilled.

FIG. 19 depicts a plot 250 of the spectral difference between thespectroscopic ellipsometry measurements depicted in FIG. 18. Plotline251 depicts the difference between measurement results for theparameter, α. As depicted in FIG. 19, the spectral differences are quitedramatic. Again, these data sets are effectively employed in amulti-target analysis to break correlations and improve measurementperformance.

In another aspect, a series of measurements are performed such that eachset of measurement data is collected from metrology target structureswhen the metrology target structures are filled with a different fillmaterial, or combinations of different fill materials. The collecteddata is combined in a multi-target model based measurement to reduceparameter correlations and improve measurement performance.

In another aspect, measurement data is collected from a metrology targetsubject to condensation when the condensation process has reached asteady state. In other words, the amount of fill provided by thecondensation process has reached steady state.

In yet another aspect, measurement data is collected from a metrologytarget subject to condensation before the condensation process hasreached a steady state. In other words, the amount of fill provided bythe condensation process is changing during the time of measurement.

FIG. 14 illustrates a method 200 for performing measurements ofstructures subject to capillary condensation. Method 200 is suitable forimplementation by a metrology system such as metrology system 100illustrated in FIG. 1 of the present invention. In one aspect, it isrecognized that data processing blocks of method 200 may be carried outvia a pre-programmed algorithm executed by one or more processors ofcomputing system 130, or any other general purpose computing system. Itis recognized herein that the particular structural aspects of metrologysystem 100 do not represent limitations and should be interpreted asillustrative only.

In block 201, a first amount of illumination light is provided to one ormore structural elements disposed on a specimen.

In block 202, a first gaseous flow including a first fill material in avapor phase is provided to the one or more structural elements duringthe illumination of the one or more structural elements. A portion ofthe first fill material is condensed onto the one or more structuralelements in a liquid phase. The portion of the first fill material fillsat least a portion of a space between one or more geometric features ofthe one or more structural elements.

In block 203, a first amount of collected light is detected from the oneor more structural elements in response to the first amount ofillumination light.

In block 204, a first set of measurement signals are generated that areindicative of the first amount of collected light.

In the embodiment depicted in FIG. 1, spectroscopic ellipsometermeasurements of metrology targets subject to a gaseous flow havingvarying amounts of liquid fill material are performed. However, ingeneral, any suitable metrology technique may be employed to performmeasurements of metrology targets subject to a gaseous flow havingvarying amounts of liquid fill material in accordance with the methodsand systems described herein.

Suitable metrology techniques include, but are not limited to,spectroscopic ellipsometry and spectroscopic reflectometry, includingsingle wavelength, multiple wavelength, and angle resolvedimplementations, spectroscopic scatterometry, scatterometry overlay,beam profile reflectometry and beam profile ellipsometry, includingangle-resolved and polarization-resolved implementations, imagingoverlay, dark field and bright field patterned wafer inspection may becontemplated, individually, or in any combination.

In one example, images of filled structures and images of the samestructures in an unfilled state are utilized in an image basedmeasurement of overlay, patterned wafer defects, etc. In anotherexample, images of filled structures alone are utilized in an imagebased measurement of overlay, patterned wafer defects, etc. In animaging overlay example, AIM targets or box-in-box targets are filledand measured and analyzed to estimate overlay errors. In these examples,an image-based analysis is employed to estimate values of parameters ofinterest.

In general, the aforementioned measurement techniques may be applied tothe measurement of process parameters, structural parameters, layoutparameters, dispersion parameters, or any combination thereof. By way ofnon-limiting example, overlay, profile geometry parameters (e.g.,critical dimension, height, sidewall angle), process parameters (e.g.,lithography focus, and lithography dose), dispersion parameters, layoutparameters (e.g., pitch walk, edge placement errors), film thickness,composition parameters, or any combination of parameters may be measuredusing the aforementioned techniques.

By way of non-limiting example, the structures measured with shapefilling include line-space grating structures, FinFet structures, SRAMdevice structures, Flash memory structures, and DRAM memory structures.

In another further aspect, the metrology targets located on the waferare design rule targets. In other words, the metrology targets adhere tothe design rules applicable to the underlying semiconductormanufacturing process. In some examples, the metrology targets arepreferably located within the active die area. In some examples, themetrology targets have dimensions of 15 micrometers by 15 micrometers,or smaller. In some other examples, the metrology targets are located inthe scribe lines, or otherwise outside the active die area.

In some examples, model-based measurements are performed with shapefilling to estimate one parameter of interest. Thus, the measurementmodel associated with the parameter of interest is optimizedindependently. By measuring each parameter of interest individually, thecomputational burden is reduced and the performance of the underlyingmeasurement can be maximized by selecting different wavelengths,measurement subsystems, and measurement methods that are optimized foreach individual parameter. In addition, different model-basedmeasurement solvers can be selected, or configured differently, for eachparameter of interest.

However, in some other examples, model-based measurements are performedwith shape filling to estimate multiple parameters of interest inparallel. Thus, the measurement model is developed to solve for multipleparameters of interest.

In some examples, measurements of parameters of interest performed at aparticular measurement site rely on data collected from that particularmeasurement site only, even though data may be collected from multiplesites on the wafer. In some other examples, measurement data collectedfrom multiple sites across the wafer, or a subset of the wafer is usedfor measurement analysis. This may be desirable to capture parametervariations across the wafer.

In some examples, measurements of parameters of interest are performedbased on filled metrology targets with multiple, different measurementtechniques including single target techniques, multi-target techniquesand spectra feedforward techniques. Accuracy of measured parameters maybe improved by any combination of feed sideways analysis, feed forwardanalysis, and parallel analysis. Feed sideways analysis refers to takingmultiple data sets on different areas of the same specimen and passingcommon parameters determined from the first dataset onto the seconddataset for analysis. Feed forward analysis refers to taking data setson different specimens and passing common parameters forward tosubsequent analyses using a stepwise copy exact parameter feed forwardapproach. Parallel analysis refers to the parallel or concurrentapplication of a non-linear fitting methodology to multiple datasetswhere at least one common parameter is coupled during the fitting.

Multiple tool and structure analysis refers to a feed forward, feedsideways, or parallel analysis based on regression, a look-up table(i.e., “library” matching), or another fitting procedure of multipledatasets. Exemplary methods and systems for multiple tool and structureanalysis is described in U.S. Pat. No. 7,478,019, issued on Jan. 13,2009, to KLA-Tencor Corp., the entirety of which is incorporated hereinby reference.

In yet another aspect, the measurement results obtained as describedherein can be used to provide active feedback to a process tool (e.g.,lithography tool, etch tool, deposition tool, etc.). For example, valuesof critical dimensions determined using the methods and systemsdescribed herein can be communicated to a lithography tool to adjust thelithography system to achieve a desired output. In a similar way etchparameters (e.g., etch time, diffusivity, etc.) or deposition parameters(e.g., time, concentration, etc.) may be included in a measurement modelto provide active feedback to etch tools or deposition tools,respectively. In some example, corrections to process parametersdetermined based on measured device parameter values may be communicatedto a lithography tool, etch tool, or deposition tool.

It should be recognized that the various steps described throughout thepresent disclosure may be carried out by a single computer system 130, amultiple computer system 130, or multiple, different computer systems130. Moreover, different subsystems of the system 100, such as thespectroscopic ellipsometer 101, may include a computer system suitablefor carrying out at least a portion of the steps described herein.Therefore, the aforementioned description should not be interpreted as alimitation on the present invention but merely an illustration. Further,computing system 130 may be configured to perform any other step(s) ofany of the method embodiments described herein.

The computing system 130 may include, but is not limited to, a personalcomputer system, mainframe computer system, workstation, image computer,parallel processor, or any other device known in the art. In general,the term “computing system” may be broadly defined to encompass anydevice, or combination of devices, having one or more processors, whichexecute instructions from a memory medium. In general, computing system130 may be integrated with a measurement system such as measurementsystem 100, or alternatively, may be separate, entirely, or in part,from any measurement system. In this sense, computing system 130 may beremotely located and receive measurement data from any measurementsource and transmit command signals to any element of metrology system100.

Program instructions 134 implementing methods such as those describedherein may be transmitted over a transmission medium such as a wire,cable, or wireless transmission link. Memory 132 storing programinstructions 134 may include a computer-readable medium such as aread-only memory, a random access memory, a magnetic or optical disk, ora magnetic tape.

In addition, the computing system 130 may be communicatively coupled tothe spectrometer 104 or the illuminator subsystem 102 of theellipsometer 101 in any manner known in the art.

The computing system 130 may be configured to receive and/or acquiredata or information from subsystems of the system (e.g., spectrometer104, illuminator 102, vapor injection system 120, and the like) by atransmission medium that may include wireline and/or wireless portions.In this manner, the transmission medium may serve as a data link betweenthe computer system 130 and other subsystems of the system 100. Further,the computing system 130 may be configured to receive measurement datavia a storage medium (i.e., memory). For instance, the spectral resultsobtained using a spectrometer of ellipsometer 101 may be stored in apermanent or semi-permanent memory device (not shown). In this regard,the spectral results may be imported from an external system. Moreover,the computer system 130 may receive data from external systems via atransmission medium.

The computing system 130 may be configured to transmit data orinformation to subsystems of the system (e.g., spectrometer 104,illuminator 102, vapor injection system 120, and the like) by atransmission medium that may include wireline and/or wireless portions.In this manner, the transmission medium may serve as a data link betweenthe computer system 130 and other subsystems of the system 100. Further,the computing system 130 may be configured to transmit command signalsand measurement results via a storage medium (i.e., memory). Forinstance, the measurement results 115 obtained by analysis of spectraldata may be stored in a permanent or semi-permanent memory device (notshown). In this regard, the spectral results may be exported to anexternal system. Moreover, the computer system 130 may send data toexternal systems via a transmission medium. In addition, the determinedvalues of the parameter of interest are stored in a memory. For example,the values may be stored on-board the measurement system 100, forexample, in memory 132, or may be communicated (e.g., via output signal115) to an external memory device.

As described herein, the term “capillary condensation” includes anyprocess by which a vaporized fill material is deposited onto structuresunder measurement in liquid form. This includes adsorption and any otherrelated physical mechanism. As such the fill material may be referred toas a condensate material or a adsorbate material, interchangeably.

As described herein, the term “critical dimension” includes any criticaldimension of a structure (e.g., bottom critical dimension, middlecritical dimension, top critical dimension, sidewall angle, gratingheight, etc.), a critical dimension between any two or more structures(e.g., distance between two structures), and a displacement between twoor more structures (e.g., overlay displacement between overlayinggrating structures, etc.). Structures may include three dimensionalstructures, patterned structures, overlay structures, etc.

As described herein, the term “critical dimension application” or“critical dimension measurement application” includes any criticaldimension measurement.

As described herein, the term “metrology system” includes any systememployed at least in part to characterize a specimen in any aspect,including measurement applications such as critical dimension metrology,overlay metrology, focus/dosage metrology, and composition metrology.However, such terms of art do not limit the scope of the term “metrologysystem” as described herein. In addition, the metrology system 100 maybe configured for measurement of patterned wafers and/or unpatternedwafers. The metrology system may be configured as an inspection toolsuch as a LED inspection tool, edge inspection tool, backside inspectiontool, macro-inspection tool, or multi-mode inspection tool (involvingdata from one or more platforms simultaneously), and any other metrologyor inspection tool that benefits from the calibration of systemparameters based on critical dimension data. For purposes of this patentdocument, the terms “metrology” system and “inspection” system aresynonymous.

Various embodiments are described herein for a semiconductor processingsystem (e.g., an inspection system or a lithography system) that may beused for processing a specimen. The term “specimen” is used herein torefer to a wafer, a reticle, or any other sample that may be processed(e.g., printed or inspected for defects) by means known in the art.

As used herein, the term “wafer” generally refers to substrates formedof a semiconductor or non-semiconductor material. Examples include, butare not limited to, monocrystalline silicon, gallium arsenide, andindium phosphide. Such substrates may be commonly found and/or processedin semiconductor fabrication facilities. In some cases, a wafer mayinclude only the substrate (i.e., bare wafer). Alternatively, a wafermay include one or more layers of different materials formed upon asubstrate. One or more layers formed on a wafer may be “patterned” or“unpatterned.” For example, a wafer may include a plurality of dieshaving repeatable pattern features.

A “reticle” may be a reticle at any stage of a reticle fabricationprocess, or a completed reticle that may or may not be released for usein a semiconductor fabrication facility. A reticle, or a “mask,” isgenerally defined as a substantially transparent substrate havingsubstantially opaque regions formed thereon and configured in a pattern.The substrate may include, for example, a glass material such asamorphous SiO2. A reticle may be disposed above a resist-covered waferduring an exposure step of a lithography process such that the patternon the reticle may be transferred to the resist.

One or more layers formed on a wafer may be patterned or unpatterned.For example, a wafer may include a plurality of dies, each havingrepeatable pattern features. Formation and processing of such layers ofmaterial may ultimately result in completed devices. Many differenttypes of devices may be formed on a wafer, and the term wafer as usedherein is intended to encompass a wafer on which any type of deviceknown in the art is being fabricated.

In one or more exemplary embodiments, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by ageneral purpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code means in the form of instructions or datastructures and that can be accessed by a general-purpose orspecial-purpose computer, or a general-purpose or special-purposeprocessor. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

Although certain specific embodiments are described above forinstructional purposes, the teachings of this patent document havegeneral applicability and are not limited to the specific embodimentsdescribed above. Accordingly, various modifications, adaptations, andcombinations of various features of the described embodiments can bepracticed without departing from the scope of the invention as set forthin the claims.

What is claimed is:
 1. A measurement system comprising: an illuminationsource configured to provide a first amount of illumination light to oneor more structural elements disposed on a specimen; a vapor injectionsystem configured to provide a first gaseous flow including a first fillmaterial in a vapor phase to the one or more structural elements duringthe illumination of the one or more structural elements, wherein aportion of the first fill material is condensed onto the one or morestructural elements in a liquid phase, and wherein the portion of thefirst fill material fills at least a portion of a space between one ormore geometric features of the one or more structural elements, whereinthe vapor injection system mixes a first flow of unsaturated purge gaswith a second flow of purge gas saturated with the first fill materialin a vapor phase to provide the first gaseous flow; and a detectorconfigured to receive a first amount of collected light from the one ormore structural elements in response to the first amount of illuminationlight and generate a first set of measurement signals indicative of thefirst amount of collected light.
 2. The measurement system of claim 1,wherein the vapor injection system is further configured to provide asecond gaseous flow including a second fill material in a vapor phase tothe one or more structural elements during the illumination of the oneor more structural elements, wherein a portion of the second fillmaterial is condensed onto the one or more structural elements in aliquid phase, and wherein the portion of the second fill material fillsat least a portion of the space between one or more geometric featuresof the one or more structural elements.
 3. The measurement system ofclaim 1, further comprising: a computing system configured to: receivethe first set of measurement signals; and estimate a value of aparameter of interest of the one or more structural elements based atleast in part on the first set of measurement signals.
 4. Themeasurement system of claim 3, wherein the estimating of the value ofthe parameter of interest involves any of a model-based regression, amodel-based library search, a model-based library regression, animage-based analysis, and a signal response metrology model.
 5. Themeasurement system of claim 1, wherein the illumination source isfurther configured to provide a second amount of illumination light tothe one or more structural elements disposed on the specimen, whereinthe vapor injection system is further configured to provide a secondgaseous flow including the first fill material at a different partialpressure than the first gaseous flow, wherein the detector is furtherconfigured to receive a second amount of collected light from the one ormore structural elements in response to the second amount ofillumination light and generate a second set of measurement signalsindicative of the second amount of collected light.
 6. The measurementsystem of claim 5, further comprising: a computing system configured to:receive the first set of measurement signals; receive the second amountof measurement signals; and estimate a value of a parameter of interestof the one or more structural elements based at least in part on thefirst and second sets of measurement signals and a multi-targetmeasurement model.
 7. The measurement system of claim 5, wherein thepartial pressure of the first fill material in the second gaseous flowis approximately zero.
 8. The measurement system of claim 1, wherein themeasurement system is configured as any of a spectroscopic ellipsometer,a spectroscopic reflectometer, an angle resolved reflectometer, a darkfield inspection system, a bright field inspection system, and animaging overlay measurement system.
 9. The measurement system of claim1, wherein the first amount of illumination light is broadband lightincluding illumination wavelengths from 100 nanometers to 2,500nanometers.
 10. The measurement system of claim 1, wherein the specimentemperature is approximately the same temperature as a temperature ofthe first fill material vaporized in the first gaseous flow.
 11. Themeasurement system of claim 1, wherein the vapor injection systemadjusts a partial pressure of the fill material in the first gaseousflow by changing a ratio of the flow of unsaturated purge gas and theflow of purge gas saturated with the first fill material in a vaporphase.
 12. The measurement system of claim 1, wherein the vaporinjection system comprises: a bubbler including the first fill materialin a liquid phase, wherein a portion of the liquid fill materialvaporizes into the second flow of purge gas to saturate the second flowof purge gas with the first fill material in a vapor phase.
 13. Themeasurement system of claim 1, wherein the fill material is any ofwater, ethanol, toluene, isopropyl alcohol, methanol, and benzene. 14.The measurement system of claim 1, wherein the first fill materialexhibits fluorescence in response to the first amount of illuminationlight.
 15. A measurement system comprising: an illumination sourceconfigured to provide an amount of illumination light to one or morestructural elements disposed on a specimen; a vapor injection systemcomprising: a first mass flow controller that regulates a flowrate of afirst flow of a purge gas; a second mass flow controller that regulatesa flowrate of a second flow of the purge gas; and a bubbler including afirst fill material in a liquid phase, wherein the second flow of thepurge gas passes through the bubbler and a portion of the liquid fillmaterial vaporizes into the second flow of the purge gas to saturate thesecond flow of the purge gas with the first fill material in a vaporphase, wherein the vapor injection system mixes the first flow of purgegas with the second flow of purge gas saturated with the first fillmaterial in a vapor phase to provide a gaseous flow; a nozzle located inclose proximity to the one or more structural elements on the specimen,wherein the nozzle provides the gaseous flow locally to the one or morestructural elements disposed on the specimen during the illumination ofthe one or more structural elements, wherein a portion of the first fillmaterial is condensed onto the one or more structural elements in aliquid phase, and wherein the portion of the first fill material fillsat least a portion of a space between one or more geometric features ofthe one or more structural elements; and a detector configured toreceive a first amount of collected light from the one or morestructural elements in response to the first amount of illuminationlight and generate a first set of measurement signals indicative of thefirst amount of collected light.
 16. The measurement system of claim 15,further comprising: a computing system configured to: communicate afirst command signal to the first mass flow controller that causes thefirst mass flow controller to adjust the flowrate of the first flow ofthe purge gas; and communicate a second command signal to the secondmass flow controller that causes the second mass flow controller toadjust the flowrate of the second flow of the purge gas such that aratio of the flowrate of the first flow of the purge gas and theflowrate of the second flow of the purge gas is adjusted to achieve adesired partial pressure of the first fill material in the gaseous flow.17. A method comprising: providing a first amount of illumination lightto one or more structural elements disposed on a specimen; providing afirst gaseous flow including a first fill material in a vapor phase tothe one or more structural elements during the illumination of the oneor more structural elements, wherein a portion of the first fillmaterial is condensed onto the one or more structural elements in aliquid phase, and wherein the portion of the first fill material fillsat least a portion of a space between one or more geometric features ofthe one or more structural elements, wherein the providing of the firstgaseous flow involves mixing a first flow of unsaturated purge gas witha second flow of purge gas saturated with the first fill material in avapor phase; detecting a first amount of collected light from the one ormore structural elements in response to the first amount of illuminationlight; and generating a first set of measurement signals indicative ofthe first amount of collected light.
 18. The method of claim 17, furthercomprising: providing a second gaseous flow including a second fillmaterial in a vapor phase to the one or more structural elements duringthe illumination of the one or more structural elements, wherein aportion of the second fill material is condensed onto the one or morestructural elements in a liquid phase, and wherein the portion of thesecond fill material fills at least a portion of the space between oneor more geometric features of the one or more structural elements. 19.The method of claim 17, further comprising: providing a second amount ofillumination light to the one or more structural elements disposed onthe specimen; providing a second gaseous flow including the first fillmaterial at a different partial pressure than the first gaseous flow;detecting a second amount of collected light from the one or morestructural elements in response to the second amount of illuminationlight; and generating a second set of measurement signals indicative ofthe second amount of collected light.
 20. The method of claim 19,further comprising: estimating a value of a parameter of interest of theone or more structural elements based at least in part on the first andsecond sets of measurement signals.
 21. The method of claim 20, whereinthe estimating of the value of the parameter of interest involves any ofa model-based regression, a model-based library search, a model-basedlibrary regression, an image-based analysis, and a signal responsemetrology model.
 22. The method of claim 17, wherein a temperature ofthe specimen is approximately the same temperature as a temperature ofthe first fill material vaporized in the first gaseous flow.
 23. Themethod of claim 17, further comprising: adjusting a partial pressure ofthe first fill material in the first gaseous flow by changing a ratio ofthe flow of unsaturated purge gas and the flow of purge gas saturatedwith the first fill material in a vapor phase.
 24. The method of claim17, wherein the fill material is any of water, ethanol, toluene,isopropyl alcohol, methanol, and benzene.
 25. The method of claim 17,wherein the first fill material exhibits fluorescence in response to thefirst amount of illumination light.
 26. The method of claim 17, furthercomprising: adjusting a degree of saturation of the first fill materialin the first gaseous flow such that any spaces between the one or moregeometric features below a desired maximum feature size are filled.